The present invention relates to magnetic recording media containing embedded servo-marks in the media and a lubricant topcoat and to a method for manufacturing such magnetic recording media. The present invention has particular applicability in forming lubricant topcoats for use in high areal recording density magnetic recording media with increased data reading speed.
Thin film magnetic recording disks and disk drives are conventionally employed for storing large amounts of data in magnetizable form. In operation, a typical contact start/stop (CSS) method involves a floating transducer head gliding at a predetermined distance from the surface of the disk due to dynamic pressure effects caused by air flow generated between the sliding surfaces of the transducer head and the disk. During reading and recording (writing) operations, the transducer head is maintained at a controlled distance from the recording surface, supported on a bearing of air as the disk rotates, such that the transducer head can be freely moved in both the circumferential and radially directions allowing data to be recorded on and retrieved from the surface of the disk at a desired position in a data zone.
In conventional hard disc drives, data are stored in terms of bits along tracks. In operation, the disc is rotated at relatively high speed, and the magnetic head assembly is mounted on the end of a support or actuator arm, which positions the head radially on the disc surface. If the actuator arm is held stationary, the magnetic head assembly will pass over a circular path on the disc, i.e. over a track, and information can be read from or written to that track. Each concentric track has a unique radius, and reading and writing information from or to a specific track requires the magnetic head to be located above the track. By moving the actuator arm, the magnetic head assembly is moved radially on the disc surface between tracks. Many actuator arms are rotary, wherein the magnetic head assembly is moved between tracks by activating a servomotor which pivots the actuator arm. A linear actuator may alternatively be used to move a magnetic head assembly inward or outward on the disc along a straight line.
To record information on the disc, the transducer creates a highly concentrated magnetic field in close proximity to the magnetic recording medium. During writing, the strength of the concentrated magnetic field directly under the write transducer is greater than the coercivity of the recording medium (known as xe2x80x9csaturatingxe2x80x9d the medium), and grains of the recording medium at that location are magnetized with a direction which matches the direction of the applied magnetic field. The grains of the recording medium retain their magnetization after the saturating magnetic field is removed. As the disc rotates, the direction of the writing magnetic field is alternated based on bits of the information being stored, thereby recording a magnetic pattern on the track directly under the write transducer.
On each track, typically eight bits form a byte and bytes of data are grouped as sectors. Reading or writing a sector requires knowing the physical location of the data in the data zone so that the servo-controller of the disk drive can accurately position the read/write heads in the correct location at the correct time. Most disc drives use embedded xe2x80x9cservo patternsxe2x80x9d of recorded information on the disc. The servo patterns are read by the magnetic head assembly to inform the disc drive of track location. In conventional disc drives, tracks typically include both data sectors and servo patterns and each servo pattern typically includes radial indexing information, as well as a xe2x80x9cservo burstxe2x80x9d. A servo burst is a centering pattern to precisely position the head over the center of the track. Because of the locational precision needed, writing of servo patterns requires expensive servo-pattern writing equipment and is somewhat of a time consuming process.
A conventional approach to the servo-sensing problem includes the use of phisical voids or depressions in the magnetic layer between tracks formed by stamping or otherwise physically marking a pattern on the disc to function as servo information. A magnetic material layer is then applied at a consistent thickness over the entire disc surface. When this type of disc is used, the distance from the magnetic head to magnetic material in the depressions is further than the distance from the magnetic head to magnetic material in the track. The increased distance both reduces the strength of the signal recorded in the depressions and reduces the contribution from the depressions to the magnetic field sensed by the read head.
While the depressions or voids formed in the disc are helpful in increasing track density, they tend to reduce the tribological performance of the disc assembly. For example, during operation of the magnetic recording medium, the slider no longer travels over a smooth surface, causing several mechanical performance drawbacks. The drawbacks include modulation of fly height when encountering servo patterns, fly height perturbations due to topography changes from the track width definition, glide defects from the stamping process, and disc distortion due to the servo patterning process. It is thus preferred to provide the servo pattern without surface topography.
The application of the protective layer and the topical lubricant assist in providing high durability and reliability of thin film recording media. In accordance with conventional practices, a lubricant topcoat is applied over the protective layer to prevent wear between the disk and head interface during drive operation.
Fluoropolyether lubricants are of particular interest in lubricating magnetic recording media. These lubricants are uniquely suited to form lubricant topcoats on magnetic media because of such properties as chemical inertness, low vapor pressure, low surface tension, high thermal stability, stability under high shear stress and good boundary lubrication properties. Among the many lubricants available, liquid perfluoropolyethers (PFPE) are the most typically used in forming topcoat lubricants on magnetic recording media.
Liquid lubrication of the disk surface encounters several problems, however, which limit its effectiveness as used in rotating storage media. For example, it is well known that non-bonded lubricants will spin off a thin film disk with a carbon overcoat. Typically, PFPE lubricants do not have a retention means so that when the disk rotates, the lubricant tends to spins off the disk. The depletion of the lubricant from the disk surface increases the friction between the disk and the read/write head.
Further, the depletion of the lubricant results in non-uniformity across the surface of the disk resulting in additional operational difficulties. For example, where the thickness is too thin, the head can cause wear on the disk surface and where the lubricant thickness is too great, the head will become stuck in the lubricant (from static friction) and the head or disk could be damaged when the head suddenly becomes unstuck due to the rotating disk.
Dominguez-Burguette et al. in U.S. Pat. No. 4,404,247 disclose anchoring a polymerizable composition directly to a metallized substrate by a complex system which includes an inner polymeric film and an outer polymeric film. The inner polymer is made from a film forming aromatic or heterocyclic polymerizable monomer and a vinyl aromatic polymer and the outer polymer contains a compound having a perfluoropolyether segment. Dominguez-Burguette et al. disclose that such a system would adequately protect a metallic thin film and teach away from the use of a hard protective coating on magnetic thin film media. Several other patents to Dominguez-Burguette et al., such as U.S. Pat. Nos. 4,526,833; 4,569,962; 4,671,999; and 4,705,699, disclose additional ingredients in creating the complex two phase polymer coating system.
Literature exists on bonding lubricants on to the surface of recording media by the application of low energy radiation. Illustrative of such art are U.S. Pat. Nos. 5,545,478 and 5,631,081 both to Lin et al., which disclose a process for bonding lubricants to magnetic media by exposing the coated media to low energy electron radiation. U.S. Pat. No. 5,030,478 to Lin et al. also discloses a process for bonding lubricants to thin film recording media by low energy radiation. U.S. Pat. No. 5,661,618 to Homola et al. approached bonding a fluoroether lubricant by exposing the lubricated disk to a plasma composed of an inert gas. These references, however, have not recognized the problems associated with patterned recording media.
Hence, a continuing need exists in the art for an improved lubricated magnetic recording medium. In particular there exists a need for a magnetic recording medium having servo-marks which occupy a reduced area of the surface of the magnetic recording medium thereby increasing available area for recording data with improved trobological performance. A need also exists for an efficient, cost-effective method of manufacturing a magnetic recording medium with a lubricant topcoat exhibiting improved tribological performance and fly-stiction.
An advantage of the present invention is a magnetic recording medium having a embedded servo-marks and increased areal recording density with improved corrosion and tribological performance and an efficient cost-effective method of manufacturing a magnetic recording medium having a lubricant topcoat with servo embedded magnetic recording media.
Additional advantages and other features of the invention will be set forth in the description which follows and in part will be apparent to those having ordinary skill in the art upon examination of the following or may be learned from the practice of the present invention. Advantages of the present invention may be realized and particularly pointed out in the appended claims.
According to the present invention, the foregoing and other advantages are achieved in part by a magnetic recording medium comprising a substrate having physically recorded servo-information, e.g. a distribution of pits or indentations therein to serve as servo-marks in the magnetic recording medium; and a means for lubricating the magnetic recording medium. Lubrication of the magnetic recording medium of the present invention comprises having a cross-linked fluoropolyether topcoat thereon. The crosslinked fluoropolymer topcoat advantageously forms a relatively immobile coating that serves to protect any metallic layers thereunder from corrosion and to facilitate planarization of the servo-patterned media.
Embodiments of the present invention include an underlayer on the substrate and the magnetic layer on the underlayer; the protective overcoat comprising one or more amorphous carbon layers and the cross-linked fluoropolyether topcoat comprising a cross-linked perfluoropolyalkylether directly on the one or more amorphous carbon layers.
Another aspect of the present invention is a method of reading from or writing on the magnetic recording medium comprising sensing one or more of the servo-marks in the magnetic recording medium with a read/write head; and
moving the read/write head to a particular position on the magnetic recording medium in response to reading the one or more servo-marks.
A further aspect of the present invention is a method of manufacturing a magnetic recording medium. The method comprises physically forming a distribution of servo marks on a substrate or magnetic layer. The marks can be formed by any method that leaves pits, voids or other indentations in the surface of the particular layer as by stamping, laser texturing, etching, micromachining, etc. The formed distribution of pits, voids, or indentations function as servo-marks capable of being sensed to enable reading magnetically recorded servo-information in a data track and accurate positioning of a read/write head on a data zone
Following the formation of the servo-information, a fluoropolyether capable of cross-linking is applied to the magnetic recording medium having a distribution of servo-marks therein and polymerized to form a cross-linked fluoropolyether topcoat lubricant.
Embodiments include forming a protective overcoat, e.g. containing carbon, over a magnetic recording medium; applying a fluoropolyether comprising one or more acrylate groups on the protective overcoat by dip coating the magnetic recording medium in a solution of the fluoropolyether and polymerizing the fluoropolyether by ultraviolet radiation, where fluoropolyether comprising a plurality of xe2x80x94(CaF2aO)nxe2x80x94 repeating units, wherein each subscript a is independently in each repeating unit an integer of from 1 to about 10 and n is an integer from 5 to about 100, e.g. from 5 to about 80.
Additional advantages and other features of the present invention will become readily apparent to those skilled in this art from the following the detailed description, wherein only the preferred embodiment of the present invention is shown and described, simply by way of illustration of the best mode contemplated for carrying out the present invention. As will be realized, the present invention is capable of other and different embodiments, and its several details are capable of modifications in various obvious respects, all without departing from the present invention. Accordingly, the drawings and description should be regarded as illustrative in nature, not as restrictive.